From memory though, xv doesn't compile from source under Xorg; it needs XFree86.n Isn't it also non-free software?

xv works under Xorg. I don't know about compiling it under Xorg, but why bother when a Slackware package works fine? I used xv for years but I haven't installed it under VL 5.8 because other programs do what xv does and do it better.

xv is not free software. It does not cost anything for personal use, but there are licensing restrictions that didn't matter to me as a home user. I am not a "free software" ideologue.--GrannyGeek

25 USD. Not at all dreadfully expensive. Of course I prefer to use 'free software' myself, and usually I work something out that I can. But Xv is in fact a really nice program, and you can have the source after all.

"You may use xv for your own amusement, and if you find it nifty, useful, generally cool, or of some value to you, your registration fee would be greatly appreciated. $25 is the standard registration fee, though of course, larger amounts are quite welcome."

That's a pretty low-key beg, and it seems to be up to you to judge whether xv is useful enough or nifty enough to you to be worth $25. Registration is required if you use xv in the course of your work.--GrannyGeek